The article explains what small state diplomacy is and how it is analyzed in the academic literature. It provides introductions to and overviews of: 1) The classical literature from Thucydides to Annette Baker Fox, Robert L. Rothstein, Erling Bjøl, David Vital, Robert Keohane, and Michael Handel. 2) General introductions to the study of small state diplomacy in theory and history. 3) Regional small state diplomacy in Europe and South Asia, Latin and South America, the Pacific and the Caribbean, Africa and the Middle East. 4) Multilateral and bilateral small state diplomacy with other small states and great powers. 5) Small state strategy including status and shelter seeking, norm advocacy, smart state strategy, and virtual enlargement as well as neutrality and niche strategies. 6) New diplomatic challenges including climate change and challenges to the rule-based international order. The article concludes with an overview of journals an online resources on small state diplomacy.